Body Diode
The diode that exists unintentionally in the structure of every power MOSFET, connected in reverse between drain and source. Even when the switch is off it passes current in the reverse direction and in an H-bridge it lets the motor current circulate during the dead time. It typically drops 0.7–1.2 V.
The body diode is not a part the designer added but a consequence arising from the silicon structure of the MOSFET. It has a benefit: a motor is an inductive load and when the switch is turned off the current needs a path to continue along. During the dead time the current circulates through the body diode of the MOSFET in the opposite arm, so no destructive voltage spike appears at the motor terminals.
The price is loss. The diode typically drops 0.7–1.2 V; at 20 A this means an instantaneous loss of 14–24 W in proportion to the conduction time. The longer the dead time, the greater this loss. In addition, body diodes generally recover slowly; the reverse current pulse they draw while turning off produces additional loss and noise.
In practice, well-designed drivers keep the dead time only as short as necessary and immediately afterwards turn on the opposite MOSFET so that the current passes through the channel. This approach is known as synchronous rectification and largely eliminates the diode loss.
The context in which this term is used: DC motor and driver fault diagnosis matrix